1. Field of the Invention
The present invention relates to a digital camera, a pixel data read-out control apparatus and method, a blur-detection apparatus and method.
2. Description of Related Art
A digital camera that displays a live-view image on a display unit such as an LCD monitor is known. Furthermore, a digital camera equipped with a hand-blur (hereinafter may simply referred to as “blur”) compensation function is also known. In order to perform such a live-view display smoothly or to perform a highly precise blur-compensation, it is desirable to update pixel data with a period of, for example, about 1/30 seconds.
However, with the recent increased number of pixels of an image pick-up element, it becomes very difficult to perform the aforementioned processing in such a short time by reading out the pixel data of all of the pixels of the image pick-up element. To cope with the aforementioned drawbacks, there has been proposed to display a live-view image in a state where the number of pixels is reduced substantially or to perform blur-detection processing by using an image pick-up element such as a CMOS sensor that can specify any pixels and read out the image data of the specified pixels and reading out the data of a plurality of specified pixels which are thinned out from all of the pixels (hereinafter, thinned-out pixels) of the image pick-up element.
According to a conventional digital cameras using thinned-out pixel data, as shown in FIG. 10, a live-view display and a blur-detection are performed by reading out the thinned-out pixel data of a plurality of pixels before the main exposure for obtaining the picked-up image. However, a live-view display and a blur-detection will become unavailable when a shutter button is pressed to start the main exposure, and then the live-view and the blur-detection will be resumed to read out the thinned-out pixel data when the main exposure is completed after reading out the pixel data of all of the pixels. In other words, there is such a drawback that a live-view display and/or a blur-detection are not performed during the main exposure.
With regard to a live-view display, Japanese Patent Laid-open Publication No. H11-205689 discloses that a periodical read-out of pixel data is continuously performed to the image pick-up element during the main exposure and the image data is stored in an image holding portion so that the storage time becomes longer than the read-out period. However, in this structure, the pixel data is not updated during the exposure and therefore a real time live-view display is not performed.
On the other hand, in a digital camera equipped with a blur-detection function, it is desirable to read out each pixel data of an image pick-up element at high speed in order to perform a proper blur-detection.
However, in cases where a CCD is used as an image pick-up element, since it is necessary to read out the pixel signal of all of the pixels for every line, there is a limitation in high-speed processing.
For this reason, another proposal has been made. According to the proposal, an image pick-up element such as a CMOS sensor that can perform a nondestructive read-out of data is used and a plurality of small area blocks are specified among all of the pixels of the aforementioned image pick-up element. Then, the data of the pixels contained in the specified block is read out in a nondestructive manner. Then, the obtained image data is utilized for a blur-detection.
For example, Japanese Patent Laid-open Publication No. H5-130489 discloses that in order to increase the speed of block matching processing, an image pick-up element such as a CMOS sensor that can perform a nondestructive read-out is used, the data of the pixels contained in the specified blocks among all of the pixels of the aforementioned image pick-up element is read out in a nondestructive manner, and then the read-out pixel data is transmitted to a block matching portion. By utilizing the nondestructive read-out of the pixel data, a blur-detection can be performed by reading out the pixel data plural times at a high-speed period during the exposure.
According to conventional digital cameras including the aforementioned prior art, high speed processing can be attained by performing the nondestructive read-out of the pixel data contained in the aforementioned specified blocks of small area. However, since a fixed pattern noise (hereinafter referred to as “FPN”) cannot be eliminated within the image pick-up element, it is difficult to perform a highly precise blur-detection because of the noise. Furthermore, there also is a problem that the exposure becomes insufficient due to the read-out of the pixel data at a high-speed period during the exposure, resulting in a decreased blur-detection level.